The present invention relates to a near-field optical head that can be used as a near-field optical read/write head or as a probe head for a scanning near-field microscope and to a method of fabricating the optical head. More particularly, the invention relates to a near-field optical head having a microscopic aperture whose size can be changed and to a method of fabricating such a near-field optical head.
A known near-field optical head is shown in FIGS. 15(a) and 15(b), where the optical head is generally indicated by numeral 200. FIG. 15(a) is a cross-sectional view of the near-field optical head 200. FIG. 15(b) is a top plan view of the optical head 200. This head 200 has a silicon substrate 201 provided with an inverted conical hole 202. The top portion of this hole 202 forms a microscopic aperture 203 having a size b less than the wavelength of light. If propagating light is made to hit this microscopic aperture 203, near-field light is generated near the aperture 203 opposite the illuminated side, because the size b is shorter than the wavelength of the light. The propagating light is laser light, for example.
Where the near-field optical head 200 is used as a near-field read/write head, near-field light produced near the microscopic aperture 203 is made to hit a recording medium so that the surface structure or material undergoes a local change. In this way, information is recorded. Otherwise, the local change of the surface structure or material is detected, thus reading information. On the other hand, where the near-field optical head 200 is used as a probe head for a scanning near-field microscope, near-field light produced near the microscopic aperture 203 is made to hit the surface of a sample, scattering the near-field light. This results in propagating light, which in turn is detected to measure the optical characteristics or topography of the sample surface.
With the above-described near-field optical head 200, it has been difficult to form the microscopic aperture 203 with a size less than 100 nm reliably. Furthermore, it has been impossible to vary the size of the aperture 203. Where the near-field optical head 200 is used as a near-field optical recording read/write head, it is necessary to move the heavy head assembly during tracking for reading signals. Therefore, it has been difficult to place the head in position accurately and quickly.
In view of the foregoing, the present invention has been made. It is an object of the present invention to provide a near-field optical head having a microscopic aperture whose size can be varied.
It is another object of the invention to provide a method of fabricating this near-field optical head.
A near-field optical head set forth in one aspect and achieving the above-described objects comprises a substrate provided with a hole whose top portion forms a microscopic aperture. An aperture-limiting means is located inside the hole. A moving means for moving the aperture-limiting means is mounted. The aperture-limiting means is moved to limit the size of the microscopic aperture.
In this near-field optical head, the aperture-limiting means is positioned inside the hole formed in the substrate. The aperture-limiting means is moved by the moving means, thereby changing the size of the microscopic aperture. Hence, the microscopic aperture can be modified to desired size.
A near-field optical head in another aspect and achieving the above-described objects comprises a substrate provided with a hole whose top portion forms a microscopic aperture and a pair of aperture-limiting means inside the hole. Moving means are mounted to move the aperture-limiting means, respectively. The size of the microscopic aperture is limited by moving the aperture-limiting means.
In this near-field optical head, the two limiting means are located symmetrically with respect to the microscopic aperture. The aperture-limiting means are moved by their respective moving means, thereby modifying the size of the aperture. Therefore, the microscopic aperture can be varied to a desired size. Since the aperture can be moved over a recording track formed on a recording medium while maintaining constant the size of the aperture by moving the limiting means in synchronism, tracking can be done.
A near-field optical head in another aspect is characterized in that the aforementioned aperture-limiting means has a bottom surface flush with the bottom surface of the microscopic aperture.
In this near-field optical head, the aperture-limiting means are so positioned that their bottom surface is flush with the bottom surface of the microscopic aperture. This permits either a recording medium or a sample to be moved toward the microscopic aperture.
A near-field optical head in another aspect is characterized in that the moving means described above is a piezoelectric actuator or an electrostatic actuator.
In this near-field optical head, the aperture-limiting means is moved using the piezoelectric or electrostatic actuator. Therefore, the microscopic aperture can be changed to a desired size easily and accurately.
A near-field optical head in another aspect comprises a substrate provided with a hole whose top portion form a microscopic aperture and an aperture-limiting means positioned inside the hole. The aperture-limiting means is heated and expanded to thereby limit the size of the microscopic aperture.
In this near-field optical head, the aperture-limiting means that expands on heating is located inside the hole formed in the substrate. On expansion, the aperture-limiting means blocks propagating light and so the size of the microscopic aperture can be modified to a desired size by expanding the aperture-limiting means. Note that the aperture-limiting means can be heated by illuminating it with propagating light, for example.
A near-field optical head in another aspect is characterized in that there is provided a heating means for heating the aperture-limiting means.
In this near-field optical head, the heating means for heating the aperture-limiting means is mounted. Therefore, the aperture-limiting means can be expanded easily and accurately. The microscopic aperture can be modified to a desired size.
A near-field optical head in another aspect is characterized in that the aforementioned aperture-limiting means consists of a high polymer having a high coefficient of thermal expansion or a high polymer sealed with a gas.
In this near-field optical head, the aperture-limiting means is a high polymer having a high coefficient of thermal expansion or a high polymer sealed with a gas. Therefore, the aperture-limiting means can be expanded efficiently with a small amount of heat. The microscopic aperture can be modified to desired size.
A method of fabricating a near-field optical head as set forth above and achieving the objects described above starts with preparing a substrate. A hole is formed in this substrate such that the top portion form a microscopic aperture. An aperture-limiting means is positioned in the hole. A moving means for moving the aperture-limiting means is mounted. The size of the aperture is limited by moving the aperture-limiting means. A support means for supporting the moving means is deposited on a surface of the substrate that faces away from the aperture. Then, a sacrificial film is deposited on the substrate and on the support means. A light-blocking film is deposited on the sacrificial film. The light-blocking film is patterned to form the aforementioned aperture-limiting means. The support means is exposed, and the moving means described above is formed on this exposed support means. Finally, the sacrificial film is removed except for its portion located inside the hole.
In this method of fabricating a near-field optical head, the hole is formed in the substrate. The support means is deposited on the substrate. The sacrificial film is deposited on the substrate and on the support means. The light-blocking film is deposited on the sacrificial film and patterned to form the aperture-limiting means. The support means is exposed, and the moving means is formed on this support means. Finally, the sacrificial film is removed. Consequently, the aperture-limiting means that can be moved by the moving means can be formed inside the hole. The microscopic aperture can be modified to desired size by moving the aperture-limiting means by means of the moving means.
A method of fabricating a near-field optical head in another aspect is characterized in that the moving means described above is a piezoelectric or electrostatic actuator.
In the above-described method of fabricating a near-field optical head, the aperture-limiting means is moved by the use of a piezoelectric or electrostatic actuator. Therefore, the aperture-limiting means can be moved easily and accurately. The microscopic aperture can be modified to desired size.
A method of fabricating a near-field optical head another aspect in starts with preparing a substrate or a base. A hole is formed in the substrate such that the top portion forms a microscopic aperture. A film of a high polymer having a high coefficient of thermal expansion is deposited inside the hole. The film is patterned to form an aperture-limiting means located inside the hole. The size of the aperture can be limited by expanding the aperture-limiting means.
In this method of fabricating a near-field optical head, the hole is formed in the substrate. The film of a high polymer having a high coefficient of thermal expansion is deposited inside the hole. The film is patterned to form the aperture-limiting means. Therefore, the aperture-limiting means that expands on heating can be formed inside the hole. The microscopic aperture can be modified to desired size.
A method of fabricating a near-field optical head in another aspect starts with preparing a substrate or a base. A hole is formed in the substrate such that the top portion forms a microscopic aperture. A first film of a high polymer is deposited at least inside the hole. A sacrificial film is deposited on the first film of high polymer and patterned. A second film of a high polymer is deposited on the sacrificial film. A hole is formed in the second film of high polymer. The portion of the sacrificial film sandwiched between the first and second films is removed, thus forming a hollow portion. A gas is injected into the hollow portion. A high polymer is deposited in the hole in the second film of high polymer, thus forming an aperture-limiting means. The aperture-limiting means is expanded to limit the size of the microscopic aperture.
In the above-described method of forming a near-field optical head, a hole is formed in the substrate. The first film of high polymer is deposited inside the hole. The sacrificial film is deposited on the first film and patterned. The second film of high polymer is deposited on the sacrificial film. A hole is formed in the second film. That portion of the sacrificial film sandwiched between the first and second films is removed using the hole. Thus, a hollow portion is formed. A gas is injected into the hollow portion. A high polymer is deposited, and the hole in the second film is closed off. Therefore, the gas is sealed in the hollow portion. An aperture-limiting means that expands on heating can be formed. The microscopic aperture can be modified to desired size by expanding the aperture-limiting means.
An optical drive as in another aspect is an optical drive having a near-field optical head equipped with a substrate provided with a hole whose top portion forms a microscopic aperture, the optical drive acting to record and/or read information to and from a recording medium. An aperture control means has an aperture-limiting means located inside the aperture and having a moving means for moving the aperture-limiting means to limit the size of the microscopic aperture by moving the aperture-limiting means. A rotational speed control means for controlling the rotational speed of the recording medium is provided. The optical drive further includes an operation mode control means for determining the combination of a data transfer rate and a recording density.
In accordance with this aspect of the invention, the read/write rates, the capacity, and other factors can be varied according to application of data recorded. Therefore, less wasteful recording and reading can be accomplished. Consequently, it is possible to set up the optical drive by taking account of the power consumption and so forth of the drive where it is regarded as a recorder. Hence, an optical drive having excellent portability can be accomplished.
An optical drive in another aspect is based on the optical drive set forth in above and further characterized in that the data transfer rate and the recording density can be selected from values distributed successively within a range defined by preset upper limit value and lower limit value.
In this aspect of the invention, the read/write rates, the capacity, and other factors can be varied continuously according to the application of recorded data. Therefore, optimal recording and reading can be done for various applications.
An optical drive as in another aspect is based on the optical drive set forth above and further characterized in that the aforementioned aperture-limiting means and rotational speed control means are operated according to the combination of the data transfer rate and recording density determined by the operation mode control means described above.
In this aspect of the invention, the size of the aperture in the near-field optical head and the read/write rates which are important for recording and reading using near-field light can be varied simultaneously. Therefore, the read/write rates, the capacity, and other factors can be varied according to application of data recorded. Therefore, less wasteful recording and reading can be accomplished. Consequently, it is possible to set up the optical drive by taking account of the power consumption and so forth of the drive where it is regarded as a recorder. Thus, an optical drive having excellent portability can be accomplished.
Other objects and features of the invention will appear in the course of the description thereof, which follows.